Described below are methods for transmitting information by radio from a transmitter to a receiver, in which symbols of a first total length are transmitted in a first time period with first useful data and in a second time period with cyclic repetitions of the first useful data.
In radio communication systems, messages, for example containing voice information, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data, are transmitted between the transmitter and the receiver via a radio interface using electromagnetic waves. In this context, the radio stations may be various kinds of subscriber stations or network radio devices, such as repeaters, radio access points or base stations, depending on the specific refinement of the radio communication system. In a mobile radio communication system, at least some of the subscriber stations are mobile radio stations. The electromagnetic waves are emitted at carrier frequencies which are in the frequency band provided for the respective system.
Mobile radio communication systems are often in the form of cellular systems, e.g. based on the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standard, with a network infrastructure including, by way of example, base stations, devices for inspecting and controlling the base stations and other network devices. Apart from these extensively organized (supralocal) cellular, hierarchic radio networks, there are also wireless local area networks (WLANs) with a radio coverage area which is normally much more limited in physical terms. Examples of different standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM.
Access by subscriber stations to the common transmission medium is regulated in radio communication systems by multiple access (MA) methods/multiplex methods. For this multiple access, the transmission medium can be split in the time domain (Time Division Multiple Access, TDMA), in the frequency domain (Frequency Division Multiple Access, FDMA), in the code domain (Code Division Multiple Access, CDMA) or in the space domain (Space Division Multiple Access, SDMA) between the subscriber stations. Combinations of multiple access methods are also possible, such as combining a frequency division multiple access method with a code division multiple access method.
To achieve the most efficient transmission of data possible, the entire available frequency band is broken down into a plurality of subcarriers (multicarrier method). The idea on which the multicarrier systems are based is to convert the initial problem of transmitting a wide band signal into transmitting a plurality of narrowband signals. This has the advantage, inter alia, that the complexity required on the receiver can be reduced. In addition, splitting the available bandwidth into a plurality of narrowband subcarriers allows a significantly higher level of granularity for data transmission in terms of distribution of the data which is to be transmitted over the different subcarriers, i.e. the radio resources can be distributed over the data which is to be transmitted or over the subscriber stations with a high degree of fineness. Particularly in the case of transmissions at a variable data rate or in the case of bursty data traffic, the available bandwidth can be put to efficient use by assigning a number of subcarriers to different subscriber stations.
An example of a multicarrier transmission method is OFDM (Orthogonal Frequency Division Multiplexing), in which pulse shapes which are approximately square over time are used for the subcarriers. The frequency spacing for the subcarriers is chosen such that at that frequency in the frequency domain at which the signal from a subcarrier is evaluated the signals from the other subcarriers have a zero crossing. The subcarriers are therefore orthogonal with respect to one another. The usually very small spacing between the subcarriers and the narrowband nature of the signals transmitted on the individual subcarriers in the case of OFDM are intended to ensure that the transmission within the individual subcarriers is generally not frequency selective. This simplifies the signal equalization on the receiver.